Optical disk reproducing apparatus having a viterbi detector

Abstract

An optical disc reproducing apparatus including a viterbi detector for an optical disc in which digital data is stored includes an optical pick-up for reading digital data stored in the optical disc and for generating a high frequency signal, an analog-to-digital converter for sampling and quantizing the high frequency signal, and a viterbi detector for decoding a quantized signal output from the analog-to digital converter and reproducing an eight to fourteen modulation (EFM)/EFM+signal. The viterbi detector includes a branch metric calculator for receiving a signal constituted of n bits, for comparing the signal with previously set three variables, and for calculating a branch metric with respect to the input signal. A path metric update and storage unit receives the branch metric, adds the branch metric to values stored therein, compares the error content of all the possible paths with each other, and stores a metric with respect to the path having the smallest amount of errors. A path memory receives the output signal of the path metric update and storage unit and generates a viterbi decoded recovery signal. A stable eight to fourteen modulation (EFM)/EFM+signal is reproduced.

What is claimed is:  
     
       1. A viterbi detector, comprising: 
       a branch metric calculator for receiving an input signal comprising n bits comprising:  
       a difference metric calculator for comparing the input signal with three predetermined variables, for obtaining the differences between the input signal and the three variables, and for generating three difference metrics, and  
       a branch metric selector for generating a plurality of branch metrics by comparing the difference metrics with each other;  
       a path metric update and storage unit for receiving the plurality of branch metrics, for adding the branch metrics to values stored therein, for comparing the error content of all the possible paths with each other, and for storing a metric with respect to the path having the smallest amount of error content; and  
       a path memory for receiving the output signal of the path metric update and storage unit and for generating a viterbi-decoded recovery signal.  
     
     
       2. The viterbi detector of  claim 1 , wherein the variables comprise a reference value, a high limit value obtained by adding a predetermined difference value to the reference value, and a low limit value obtained by subtracting the predetermined difference value from the reference value and the reference value is represented by 2 n−1 , where n is the number of bits in the signal. 
     
     
       3. The viterbi detector of  claim 2 , wherein the variables are previously set. 
     
     
       4. The viterbi detector of  claim 1  wherein the branch metric selector generates the plurality of branch metrics by comparing respective values of the difference metrics with each other, and assigns values to the plurality of branch metrics based on a result of the comparison. 
     
     
       5. The viterbi detector of  claim 1  wherein the plurality of branch metrics generated by the branch metric selector are of a number that is greater than the number of difference metrics. 
     
     
       6. The viterbi detector of  claim 5 , wherein the number of branch metrics generated by the branch metric selector is five. 
     
     
       7. An optical disc reproducing apparatus for an optical disc in which digital data is stored, comprising: 
       an optical pick-up for reading digital data stored in the optical disc and generating a high frequency signal;  
       an analog-to-digital converter for sampling and quantizing the high frequency signal to generate an input signal comprising n bits; and  
       a viterbi detector for decoding the input signal provided by the analog-to-digital converter and reproducing an eight to fourteen modulation (EFM)/EFM+ signal,  
       wherein the viterbi detector comprises:  
       a branch metric calculator comprising:  
       a difference metric calculator for comparing the input signal with three predetermined variables, for obtaining the differences between the input signal and the three variables, and for generating three difference metrics; and  
       a branch metric selector for generating a plurality of branch metrics by comparing the difference metrics with each other:  
       a path metric update and storage unit for receiving the plurality of branch metrics, for adding the branch metrics to values stored therein, for comparing the error content of all the possible paths with each other, and for storing a metric with respect to the path having the smallest amount of error content; and  
       a path memory for receiving the output signal of the path metric update and storage unit and for generating a viterbi decoded recovery signal.  
     
     
       8. The optical disc reproducing apparatus of  claim 7 , wherein the variables comprise a reference value, a high limit value obtained by adding a predetermined difference value to the reference value, and a low limit value obtained by subtracting the predetermined difference value from the reference value, and the reference value is represented by 2 n−1 , where n is the number of bits in the signal. 
     
     
       9. The optical disc reproducing apparatus of  claim 8 , wherein the variables are previously set and are stored in a micro controller. 
     
     
       10. The optical disc reproducing apparatus of  claim 7 , further comprising an adaptive equalizer for compensating for the distorted high frequency component of the input signal of provided by the analog-to-digital converter and for transmitting the compensated high frequency component to the viterbi detector. 
     
     
       11. The optical disc reproducing apparatus of  claim 7 , wherein the branch metric selector generates the plurality of branch metrics by comparing respective values of the difference metrics with each other, and assigns values to the plurality of branch metrics based on a result of the comparison. 
     
     
       12. The optical disc reproducing apparatus of  claim 7 , wherein the plurality of branch metrics generated by the branch metric selector are of a number that is greater than the number of difference metrics. 
     
     
       13. The optical disc reproducing apparatus of  claim 12 , wherein the number of branch metrics generated by the branch metric selector is five.